Spirolactones are bicyclic compounds having one carbon atom common to both cyclic ring structures wherein each cyclic structure is a lactone. A lactone is a heterocyclic ring structure containing an oxygen in the cyclic ring and a ketone group on a cyclic carbon adjacent to the hetero oxygen atom. Spirolactones have been suggested for use as a thermoplastic hydrogel by reacting a spirolactone with a difunctional active hydrogen compound such as proposed in U.S. Pat. No. 4,064,086.
It now has been found that a thermosetting polyspirolactone polymer structure preferably containing two or more spirolactone structures can be cross-linked with a diamine or triamine or similar polyamine to produce an excellent cured surface coating composition. The polyspirolactone polymer can be a moderately low molecular weight polymer which is particularly suitable for high solids coatings. The coating composition can be produced by reacting an oxirane resin such as a diepoxide resin with a lower alkyl malonate such as diethyl malonate in the presence of a catalyst to produce a polyspirolactone polymer. The polymer structure is then mixed with a polyamine which is adapted to heat-cure and cross-link the polyspirolactone polymer by opening two or more of the lactone ring structures to form amide linkages.